(1) Field of the Invention
This invention relates to key actuators and other switching devices and, more particularly, to key actuators and other switching devices actuators molded of conductive loaded resin-based materials comprising micron conductive powders, micron conductive fibers, or a combination thereof, homogenized within a base resin when molded. This manufacturing process yields a conductive part or material usable within the EMF or electronic spectrum(s).
(2) Description of the Prior Art
Key actuators and other electrical switching devices are used in many applications. Such switches are often the primary means of control for machines, mechanisms, computers, tools, and communications devices. Key actuators are found in standard computer keyboards, mobile and stationary telephones, industrial controls, human-machine interfaces, calculators, musical instruments, and PDA devices, among other applications. Other simple switches are found on computer mice, appliances, computer joysticks, manual machine controls, control grips, and the like.
All switches are essentially binary transducers that are either in an open state or in a closed state. In the open state, switches may have almost infinite impedance. In the closed state, the impedance drops to almost zero impedance. The binary character of switches is well-suited to digital computing technology wherein each switch state can be assigned a ‘0’ or a ‘1’ designation.
A large number of switching mechanisms are found in the art. In contact switches, a circuit is opened or closed by direct contact between conductive elements. This is the method used in a residential lighting switch. The conductive elements can be metal wires, traces, brushes, tabs, or the like. Alternatively, liquid metal, such as in the case of a mercury switch, can be used as the direct contact path. Indirect switching methods are also used. For example, a magnetic reed switches, hall effect switches, and ferrite core switches use magnetic fields to control conductive paths. Another important indirect switching technique is capacitance switching. In a capacitance switch, the open and closed states correspond to two different capacitance values that the switch may exhibit. A sensing circuit is used to distinguish the capacitance value, and therefore the state, of the switch.
Of particular importance to the present invention are the switching mechanisms used in most keypad switches: direct contact (conductor-to-conductor) and indirect contact (capacitance-based). In either case, the keying mechanism is based a first conductor, typically attached to the underside of the keypad, and a second conductor, typically located on a circuit board underlying a particular keypad in the array of keypads. In a direct contact keying mechanism, when the keypad is pressed, the first conductor on the keypad is forced into direct contact with the second conductor on the circuit board matrix to complete a circuit. A digital decoding integrated circuit then decodes this completed circuit to determine which key was pressed. In the case of the capacitance-based, indirect contact, the effect of pressing the keypad is to reduce the distance between the first conductor and the second conductor. The first and second conductors from the plates of a capacitor. In the pressed state, the plates of the capacitor are closer and, therefore, the capacitance of this matrix location is increased. The digital decoding integrated circuit detects this change in capacitance using, for example, a RC time-constant measurement.
In either the direct or indirect switching case, the keypad and circuit board matrix contacting conductors are found to comprise metals, such as copper, silver, gold, and the like, or conductive inks, or carbon pills. Conductive ink is typically silk screen printed onto the circuit board and/or the underside of the keypad. Carbon pills are typically used on the underside of the keypad. Carbon pills are carbon, or graphite, tablets that are molded into the keypad. Alternatively, carbon pills may comprise carbon impregnated silicon rubber.
Other switching actuators, such as rotary switches, toggle switches, push-button switches, and rocker switches, such as found in some light switches, are also of importance to the present invention. The switching contacts in these switching actuators are more typically metal-to-metal although conductive inks and carbon pills may also be used.
Several prior art inventions relate to key actuators and other electrical switching devices. U.S. Patent Application 2001/0025065 to Matsumora teaches an encoder switch comprising a rotating code disk with a conductive resin pattern formed thereon. The conductive resin comprises a resin material further comprising silver powder, silver-coated carbon beads, or both silver powder and silver-coated carbon beads. Phosphor bronze brushes are used to contact the code disk pattern. U.S. Patent Application 2003/0203668 to Cobbley et al discloses an electrical interconnect device. The interconnect device comprises a conductive resi/catalyst system disposed between two conductive plates. As the plates are forced toward each other, insulating coatings around the conductive particles in the resin are broken to thereby expose the conductive particles. The interconnecting path is formed by these conductive particles. U.S. Pat. No. Re. 34,642 to Maenishi et al shows an electric contact switching device comprising, in part, a non-conductive resin. U.S. Pat. No. 6,362,976 to Winters et al describes a keypad comprising silicone buttons over silicone domes. When depressed, the silicone buttons deform the silicone domes to cause carbon pills to contact across traces on a printed circuit board. The contacting carbon pills short traces together. U.S. Pat. No. 4,503,410 to Hochreutiner describes an electromagnetic relay device having two contact pills each comprising an electrically and magnetically conducting material.